In the Dark

In the Dark

Two kilometres below the earth in a mine in Northern Ontario two very different sets of explorers carry out vastly different searches. There are miners extracting the nickel the area is famous for, and scientists – what they are looking for has so far been impossible to find.

A photo of SNO+ taken by one of the underwater cameras in the SNO+ cavern.

Less than one hundred years ago Fritz Zwicky, a Swiss astronomer, realized that the universe contained far more matter than could be seen. Dubbed dark matter because it does not absorb, reflect or emit light, the only way we know it exists is because we can observe the effects it has on other objects. Dark matter is the reason astronomers see light bend in space or why some stars seem to orbit their galaxies faster than they should.

As one of the world’s deepest underground labs SNOLAB in Sudbury, Ontario has been designed to give it an advantage when searching for dark matter. Dark matter particles are extremely hard to detect because they are drowned out by cosmic rays, those waves and particles that rain down on earth from space. Dark matter particles pass through regular matter without interacting, however. This means that while cosmic rays are filtered out by the two kilometres of rock above SNOLAB, the dark matter reaches the detectors in the lab. 

Fast fact: We have only identified about five per cent of what makes up the universe. Dark matter makes up about 27 per cent while 68 per cent of the universe is dark energy.

SNOLAB teams try to detect dark matter using advanced methods and different materials. For example:

A SNOLAB engineer in training working in the SNO+ control room.

PICO uses a bubble chamber, a large cylinder filled with liquid at the exact pressure and temperature to cause it to boil if the right particle passes through it.

DEAP uses a detector filled with liquid argon, a substance that emits flashes of light if a particle passes through it. 

Despite the great efforts being made to solve the riddle of dark matter scientists have yet to identify what it is. Many scientists believe it may be a particle that has not been discovered. Huge amounts of such an unidentified particle might account for the excessive gravitational forces being observed out in the universe. There are also scientists that believe dark matter could also simply be gravity itself and that we have not been correct in what we know about gravity. It may be that we are looking for a particle that does not exist at all!

Inset: In the 1960’s American astronomer Vera Rubin made groundbreaking observations that provided evidence for the existence of dark matter in the universe.

Article originally published in Brainspace Magazine

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